Everybody makes mistakes during taijiquan practice. This
is quite normal and human.
Once you become aware of a mistake it is usually easy to correct.
Ultimately, a student learns to feel when they are making a mistake and then
correct it themselves.
At this point, they are responsible for their own practice.
Some faults are more serious than others and could lead to injury;
especially during a combat situation.

Gaps

Gaps are holes in your practice that can be exploited by an opponent.
A gap may be caused by poor postural alignment, leaving a leg behind when
you step or failing to complete an application.
Every mistake represents an opportunity.
It is essential that we spot those gaps in the class and correct them.

Enter each situation without telegraphing your arrival and leave without a
trace.

(Barefoot Doctor)

Deficiencies

A deficiency is a lack and in taijiquan this typically
refers to:

Accuracy

Awareness

anticipation

Emotional instability

Failure to yield

No
groundpath

No
neigong

Poor
connection throughout the body

Poor
footwork

Tensing the muscles

Deficiencies are qualities that weaken the way in which you practice taijiquan.
They need to be identified and corrected.
Gaps and deficiencies can cripple your combat abilities.

Identify

Your master cannot reasonably spot all of your mistakes, so it
is important to enlist the help of your practice partner.
If you are making a mistake they need to tell you in a friendly way and
offer help if you need it.

Contact

Tolkien wrote "the burned hand
teaches best". Partner work must involve physical contact.
If you succeed in escaping, only to forget about your opponent, a gentle
slap reminds you.
If you evade a punch, but leave yourself wide open, a second blow will
remind you.
A playful tap is much more memorable than a conversation and takes far less
time.

Corrections

Some people look unhappy when they are corrected. Others
look irritated.
It is important to consider why you are being corrected...
Taijiquan is not competitive or petty.
Your teacher corrects you because they care about your progress and
wellbeing.

Lack of correction

Uncorrected practice can lead to injury.
Accept the correction with good grace and courtesy.
You can learn from it.

No plateaus

Taijiquan practice can always be improved; there is no conclusion to the
training, no place to rest.
You will never reach a 'plateau' unless you stop the discipline.
Do not become arrogant, defensive or emotionally-invested in your practice.

Unavoidable gaps and deficiencies

Once you are capable of performing the taijiquan without making obvious mistakes, it is necessary to become aware of flaws in
the system.
Every combat application has areas of weakness and you must know what they
are.
These cannot be patched by improving your pattern of movement.
It is simply not possible to offer the perfect counter to every conceivable
attack.
You must simply accept the flaws and learn how you can compensate for their
existence.

Small san sau

Small san sau is the first exercise that explores how to use gaps and
deficiencies to your advantage.
It uses relative positioning to offer holes in the defences and trick the
opponent into attacking.
This approach is taken from the Art of War; apparent weakness is utilised to
lure the opponent closer.
The later syllabus takes this much further.

5 challenges

The first major test of your ability to adapt is the 5
challenges.
From the very first challenge you must demonstrate an awareness of your
weaknesses and how to compensate for them.

Look to your own faults,
What you have done or left undone.
Overlook the faults of others.